Volvo D12 pressure in expansion tank. I checked for exhaust Gas, its fine.

First thing to do is pressure test the coolant system for leaks, don't throw parts at it. take a coolant and oil sample and lets find out where the coolant is going first.

 

I have same problem now, after removing air compressor couple of time due to a bad gaskets, a have put a part this thing many time, then gaskets went bad you would have coolant in air system, air pressure build up in coolant system or bouth . All you need is new gaskets on air compressor but Volvo in North America is not selling gasket kits for it, fording us to buy whole unit, this is BS.
Gasket kits are widely available in Eastern Europe, Asia but not here.
For now I have to use liquid gasket from Canadian tire, it's hold for 6 month or so.

 

Did you find your problem with the over pressuring in your expansion tanks? I have the same problem. I changed the cups yesterday and left the dealer with the exact same problem. They are now suggesting head gasket or worst. We checked the compressor, egr cooler and both are fine. Thing is it looks like I gotta open up my D12.

 

My coolant is draining thru the reservoir hose... any ideas???